1. Field of the Invention
The present invention relates to multiple metal-insulator-metal (MIM) capacitors and a method of fabricating the same.
2. Description of the Related Art
Semiconductor devices fabricated using BIPOLAR, BICMOS and CMOS technologies require integrated capacitors having high voltage linearity, accurate capacitance values, and low parasitic capacitance. The conventional MOS or MIS capacitors which have been employed to date not only have unsatisfactory voltage linearity on account of voltage-induced space charge regions, but also widely varying parasitic capacitance.
To avoid these limitations, polysilicon-insulator-polysilicon (PIP) capacitors have recently become popular. However, since the PIP capacitors use conductive polysilicon for an upper electrode layer and a lower electrode layer, an oxidation reaction occurs at interfaces between the upper and lower electrodes and the dielectric layer, resulting in the formation of a native oxide film, which can lead to an overall reduction in capacitance. One approach to addressing this problem is to use metal-insulator-metal (MIM) capacitors.
MIM capacitors are used in many mixed-signal (MS) (analog/digital) and radio frequency (RF) circuit applications. An MIM capacitor for mixed-signal applications requires superior VCC and leakage characteristics, and an MIM capacitor for RF applications requires a high quality factor (Q value).
To this end, a dielectric layer of an MIM capacitor used in MS applications is formed to be thicker than that of an MIM capacitor used in RF applications. As a result, the capacitance per unit area of the MIM capacitor for MS applications is higher than that of the MIM capacitor for RF applications. Also, the resistance of an electrode of the MIM capacitor for RF applications requiring a high Q value should be lower than that of the MIM capacitor for MS applications.
In many cases, MIM capacitors requiring those different characteristics should be formed in the same interconnect level of the same device. However, since the thicknesses of dielectric layers of the MIM capacitors are the same in the same interconnect level, the capacitance values per unit area of the MIM capacitors are also the same, causing an unnecessary increase in the thickness of the MIM capacitor for RF applications and thus an increase in the total chip size, which can lead to degradation of the Q value.